(a) Field of the Invention
The present invention relates to a shift register and a gate driving circuit of a display device using the same, and more particularly to a shift register which can adjust a scan direction in the case where a screen of a display device is upside down, and a gate driving circuit of the display device using the same.
(b) Description of the Related Art
A display device that has recently been applied to a portable terminal may display images on a screen, a position of which is reversed, for example upside down or left and right, in accordance with a user's intention. In this case, a gate driving circuits of the display device need to be designed to change a scan direction and then output an image.
A conventional shift register, for example disclosed in Korean Patent No. 10-1020627, includes a plurality of thin film transistors (TFT).
FIG. 1 is a block diagram of a gate driving circuit, showing connection among the conventional shift registers capable of adjusting the scan direction.
FIG. 2 is a detailed circuit diagram illustrating an example of the conventional shift register shown as a block in FIG. 1.
Referring to FIG. 2, the conventional shift register includes an input unit 1 for receiving an input signal for the shifting operation, an inverter unit 2 for making off-characteristics of an output terminal better, a output unit 3 for outputting a scan input signal to a gate line, and a reset unit 4.
The input unit 1 receives a pulse input signal and transmits it to a P node (boosting node), and the inverter unit 2 inverts the signal of the P node, received from the input unit 1 and outputs the inverted signal to an X node.
In the conventional shift register, a TFT TB constituting the inverter unit 2 keeps always turned on by a high level voltage Vbias (a bias voltage), and thus there is a limit to invert the voltage of an X node on the contrary to the voltage of the P node.
Therefore, the conventional inverter unit 2 further need to include two TFTs TD and T1 in addition to the TFTs TB and TC, i.e., includes a total of four TFTs in order to compensate for insufficient driving performance for the TFTs and to secure reliability, and an LVGL signal is added to enhance the reliability.
Like this, the conventional shift register needs a plurality of thin film transistors and signal lines to improve the off-characteristics.
This causes a problem of enlarging a dead space of a display device, resulting in the display having bigger size than originally planned and modifying a structure of the gate driving circuit.
Further, a shift register of a recent gate driving circuit has additionally included a bidirectional driving function that changes order of supplying a signal to the gate line in accordance with rotation of a display screen. To this end, as shown in FIGS. 1 and 2, the conventional shift register has to include a scan direction adjuster 5 including four TFTs Tb, Tbr, Tf and Tfr. Thus, as the number of transistors increases for changing the order of supplying the signal to the gate line, the conventional shift register exacerbates the foregoing problems.